A beef cattle producer, located at Eureka NSW (near Lismore), reported to the North Coast LHPA the death of wild birds on his farm. The deaths began in mid January 2013 and all the birds were being found in one particular paddock. By 22nd January there had been a total of 22 wild bird mortalities including ten crows, eight magpies, two egrets, one ibis and one peewee. In addition a domestic chicken was found dead near the farmer's house on the 21st January.
In December 2012 an aborted bovine foetus had been found by the farmer. The foetus was examined by a District Veterinarian and found to have a crown rump length of 40cm and limb deformities. Subsequent laboratory testing on the foetus was negative for Pestivirus antigen and no abnormalities were found on brain histopathology. Before a diagnosis was established for the wild bird mortalities it was considered that this bovine disease event might be related to the wild bird deaths. The NSW Department of Primary Industries (NSW DPI) Wildlife Coordinator suggested that a possible differential for both avian and bovine disease events could be arboviral disease.
Investigating this disease event was a collaborative between the North Coast LHPA, NSW DPI, NSW Office of Environment and Heritage (NSW OEH) and the Australian Wildlife Health Network (AWHN). The North Coast LHPA played a role in communicating with the farmer and receiving birds from the field to process and send to the State Diagnostic Laboratory. NSW DPI, through their NSW Wildlife Coordinator, also communicated with the farmer but in addition also undertook a liaison and coordinating role to determine what tests should be carried and what the funding source should be. NSW DPI through the State Diagnostic Laboratory excluded and reported on relevant notifiable diseases. The OEH financed the costs of tests that were not notifiable diseases. The AWHN provided technical comment on the disease event.
All birds were either found dead or showed a very short illness of paresis and paralysis before death. Most of the birds were in good body condition. Gastrointestinal or respiratory signs were not observed in any of the birds.
A veterinary pathologist from the State Diagnostic laboratory undertook a necropsy on six of the birds as part of two laboratory submissions.
Submission One (21st January):
"3 wild birds received and examined. No 1 a crow, No 2 magpie, No 3 a butcher like bird. They thawed out during transport. Necropsy findings were similar in all 3. All dehydrated in moderate body condition with some fat reserves. No signs of trauma, respiratory infection or diarrhoea. There is red, haemolytic staining of internal organs (they have been frozen), and a moderate autolysis, advanced in the intestines. All had some fibrous gizzard content and yellow pasty intestinal content. No internal parasites seen. No gross abnormalities in internal organs suggestive of virulent AI/NDV.
Female chicken, in lay. Good body condition. No sign of diarrhoea, upper respiratoryinfection. Moderate amount of fibrous/seedy ingesta in crop, gizzard, moderate amount of pasty intestinal content. Mild diffuse cloudy change in airsacs. A fully developed broken egg in the oviduct (trauma?). Internal organs appeared normal."
Submission Two (22nd January)
"No 1 - Ibis: Moderate body condition, no trauma or external abnormalities seen. No signs of diarrhoea or upper respiratory tract infection. Gizzard half full with plant material no seeds present. Internally no abnormalities seen, organs are in normal shape, size and colour. Small amount of pasty ingesta in intestines. No internal parasites detected.
No 2 - Magpie: Moderate body condition. Externally no abnormalities detected, no sign of diarrhoea or upper respiratory tract infection. Internally gizzard full with fibrous plant material, liver slightly enlarged with multiple 1 to 2 mm in diameter white yellow spots over the surface. Spleen moderately enlarged with similar creamy spots on its surface. No parasites in gastrointestinal tract"
The pathologist commented that the necropsy findings on the majority of the birds were inconclusive and may suggest a poisoning or other environmental condition such as heat stress. The necropsy findings in the chicken were considered to be from trauma but a poisoning or acute/peracute egg peritonitis could not be excluded. One of the magpies was reported as having a hepatitis and splenitis.
All birds tested negative for Influenza A and Newcastle Disease on PCR testing. A bacterial culture undertaken on the liver from the magpie was negative. Gizzard contents from five birds were tested for a range of organic chemicals. All were positive for diazinon. All other toxicity results were normal. The diazinon results ranged from 1200µg/kg to 1800µg/kg.
Diazinon toxicity was diagnosed as the cause of the wild bird deaths. The aborted fetus and chicken death were considered to be unrelated to the wild birth deaths.
Diazinon is an organophosphate chemical with an anticholinesterase mode of action. It is used extensively to control flies, lice, insect pests of ornamental plants and food crops, as well as nematodes and soil insects in lawns and croplands. Diazinon degrades rapidly in the environment, with half-time persistence usually less than 14 days. But under conditions of low temperature, low moisture, high alkalinity, and lack of suitable microbial degraders, diazinon may remain biologically active in soils for 6 months or longer. Diazinon has previously been implicated in wild bird deaths in many regions of the world (Balcomb et al, 1984; Franson and Smith, 1999; Gordon and Field, 2006; Kwon et al, 2004). Birds are more susceptible to diazinon toxicity than mammals (Walker, 1983).
The literature reports a large range of potential LD-50's for diazinon in different species of birds. An acute oral LD-50 of 2,500 to 3,500 µg diazinon/kg body weight has been determined for some birds (Eisler, 1986). Vyas et al (2006) reported mortalities within 2 hours of exposure to 1000 ppm of diazinon in the feed of Canadian geese. Specific toxicity data is not available for the species involved in this case study. However the levels of diazinon in this case study of 1.2 to 1.8 mg/kg gut content are considered to be significant because they were found in all three birds tested, they represent the minimum level that the birds were exposed to and the level detected is close to reported LD-50's in other birds and to the toxic dose determined by Vyas et al (2006). In addition a range of other differentials were excluded.
The source of the diazinon was not located. The beef farmer had not used this chemical for over 12 months - well over the relatively short half life of diazinon. He did own a five litre bottle of diazinon but it was safely secured in his shed. The cattle had organophosphate ear tags against buffalo fly but these did not contain diazinon and were considered an unlikely source of a toxic dose for wild birds.
At least one neighbouring farmer uses the product Coopers Di-Jet to control flies on their cattle. This is a potential source of the diazinon that poisoned the birds as the product was used for fly control in January.
Unfortunately anecdotal historic reports from both Australia and overseas suggest that some farmers deliberately poison wild birds by the use of diazinon or other organophosphate products. Sometimes this is done by spraying a ruminant carcass with diazinon to kill scavenging birds. In NSW, illegal baiting carries penalties of up to two years' jail and fines of over $24,000 under both the Wildlife Act 1975 and Prevention of Cruelty to Animals Act 1986, and fines of over $11,000 under the Drugs, Poisons and Controlled Substances Act 1981.
The reason why all the birds died in one paddock may simply have been because this paddock had particular environmental features of water and food that supported ibis, herons, crows and magpies. Weather preceding the mortalities had been both wet and hot with a number of days above 35°C. This may have contributed to the mortalities but is not considered a major factor compared to diazinon toxicity.
The potential links between wildlife, human and livestock disease are well recognized. This NSW disease event provides a good example of how frontline government livestock health staff can collaborate effectively with other agencies to both exclude notifiable livestock diseases and determine alternate diagnoses for local wildlife disease events.